Method of manufacturing electrical apparatus



Aug.- 23, 196 0 P. D.' PAYNE, JYR 0,

METHOD OF MANUFACTURING ELECTRICAL APPARATUS Filed Aug. 25; 13s:

INVENTOR. P190! 0. P1970! J/f.

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ilnited States Patent F METHGD OF MANUFACTURING ELECTRICAL APPARATUSPaul D. Payne, Jr., Lansdale, Pa., assiguor to Philco Corporation,Philadelphia, Pa., a corporation of Pennsylvania Filed Aug. 25, 1953,Ser. No. 376,345

'12 Claims. (Cl. 96-34) The present invention relates to improvements inmethods of manufacturing cathode ray tube screen structures and, moreparticularly, to improvements in methods of manufacturing cathode raytube screen structures of the kind which have different portions made ofmaterials which are differently responsive to electron beam impingement.

While different specific forms of such screen structures are suitablefor a wide variety of applications, the form which has been receivingthe most careful attention in recent times is that which is particularlysuitable for use as the image reproducing screen of a color televisionpicture tube. in this form, the screen structure consists of solidtranslucent substrate, which may be either the glass face plate of thecathode ray tube itself or an additional glass plate separatelysupported within the cathode ray tube envelope, and having differentportions of its beam confronting surface coated with phosphors emissiveof light of different primary colors, such as red, green and blue, forexample. In a preferred embodiment of such a screen structure, thedifferent colored light emissive phosphors take the shape of narrow,parallel strips, adjacent strips being made of phosphors emissive oflight of ditferent colors so that, proceeding in a direction transverseto the longitudinal dimensions of these strips, red, green and bluelight emissive phosphor strips, for example, will be encountered inrecurrent succession. Of course, other configurations of phosphorelements have also been found useful as, for example, one in which tinyphosphor dots are disposed in triangular groups of three, each member ofeach group of dots being made of a phosphor emissive of light of aparticular primary color and different ones of these dots being emissiveof light of different colors. The selection of the best phosphor elementconfiguration depends upon a variety of factors including the nature ofthe signal which is used to control the intensity of the cathode raybeam with which the finished screen will eventually be scanned and thenature of the system which is provided for maintaining exact coincidencebetween the instants of time at which this cathode ray beam isrepresentative of intelligence concerning a particular image color andinstants at which the beam is impinging upon phosphor elements of thescreen structure which are emissive of light of that particular color.In one such system the differently colored light emissive phophors arearranged in the aforetioned strip-like pattern and their cathode ra beamconfronting surfaces are covered with an electron permeable film made ofsome conductor such as aluminum, for example. On top of this aluminumfilm there are then deposited so-called indexing strips, preferably onefor each group of three differently colored light emissive phosphorstrips, these indexing strips being made of a material whose secondaryelectron emission ratio is substantially different from that of thealuminum. As the electron beam, in scanning its raster on this screenstructure, traverses successive groups of three differently coloredlight emissive phosphor strips, it also traverses suc- 2,950,193Patented Aug. 23, 1950 ice cesive indexing trips and intervening regionsof bare aluminum. The variations in secondary emission current whichoccur by reason of alternate beam traversals of indexing strips and barealuminum are sensed by an external circuit and are utilized to controleither the rate of scran of the electron beam across successive groupsof three phosphor strips, or the rate of application of colored lightintelligence representative signal portions to the beam intensitycontrol electrode of the cathode ray tube, or both. The specific mannerof utilizing the signals produced by these indexing strips has nobearing on the invention under consideration and need therefore not bediscussed in detail.

While various methods are known for forming the different types ofscreen structures hereinbefore briefly described, the one which has beenused with the greatest success involves the deposition of the variousphosphor and/or indexing material particles by a photographic process.This process was initiated by depositing, on the glass substrate, alayer of photosensitive gel in which there had previously beendistributed particles of one of the three colored light emissivephosphors. This gel was exposed to illumination through translucentportions in a mask, the translucent portions having the sameconfiguration as that in which it was desired to dispose, in the finalscreen structure, the screen elements of the particular phosphor beingprocessed. As a result of this exposure, the portions of the gel whichhad been illuminated became insoluble in water, while unilluminatedportions remained water soluble, as before. The screen was then washedwith water, thereby removing the unexposed portions of the gel and alsothe phosphor particles distributed therein. There remained in placethose portions of the gel, and the phosphor particles distributedtherein, which had been exposed and thereby rendered insoluble Nextthere was applied another layer of gel having distributed thereinparticles of a second one of the three different phosphor materials.This second layer of gel was again exposed to illumination throughtranslucent portions in a mask having such configuration as to produceexposure of the gel in the particular configuration in which it wasdesired to dispose the elements of the second phosphor in question. Inpractice it was often possible to use the same mask for this secondexposure as was used for the exposure of the first deposited gel, itbeing necessary, of course, to relocate this mask between exposures sothat the translucent portions thereof were aligned with differentregions of the transparent substrate during successive exposures. Thissecond exposure was also followed by washing to remove the unexposed geltogether with the phosphor particles distributed therein. A third layerof photosensitive gel was then applied, this one bearing particles ofthe third phosphor material to be deposited on the substrate. This thirdlayer of gel was again exposed through a suitably positioned mask andthe unexposed portions thereof washed away. The foregoing method ofdepositing phosphor strips in a predetermined pattern is described inmore detail in the copending US. patent application of John W. Tiley,Serial No. 248,356, filed September 26, 1951, and assigned to theassignee of the present invention. The deposition of the phosphor stripshaving thus been completed, there was next applied the aforementionedelectron permeable aluminum film by conventional techniques, and finallythere was applied still another layer of photosensitive gel. This latterlayer of gel was dried and was then covered with a layer of indexingmaterial particles. This final layer of gel was then exposed, in amanner similar to that in which the phosphor bearing gel layers wereexposed and preferably through the same mask as the latter, this maskhaving, if necessary, been repositioned again so as to expose portionsof the indexing material bearing gel in the desired geometricalrelationship to the st ips of phosphor materials beneath the aluminumfilm. Again unexposed portions of the gel weredissolved and removed,after which theentire screen structure was dried and baked, therebyvaporizing those portions of the photosensitive gels which had beenrendered insoluble by exposure .and which had therefore remained inplace in spite of the repeated washing operations.

Screen structures manufactured by the process hereinbefore brieflyoutlined, while satisfactory in some respects, were uniformlycharacterized by having phosphor elements with irregular, or fuzzyedges. This seemingly minor imperfection proved to be asource of seriousdiffieulties because, in a practicalscreen structure, the individualphosphor strips are extremely small and are closely crowded together. Itis, for example, common to position. :a group of three phosphor stripsemissive of light of different colors, side by side, within a regiononly45 mils wide and with each individual phosphor strip only. approximatelyl mils wide. In this arrangement, spaces about mils wide were leftbetween adjacent phosphor strips to enhance the purity of the colorsreproduced on the screen structure. Alternatively, adjacent phosphorstrips were sometimes located substantially contiguously, with noappreciable spaces between them. In the case of contiguous phosphorstrips, irregularities in their adjoining edges caused overlapping ofthe difierent phosphorswith the result that no sharp line of demarcationcould be maintained between beam impingement on phosphor strips of onecolor and on phosphor strips of a different color. With spaced phosphorstrips, on the other hand, irregularity of the strip edges causedunpredictable reductions in the improvement in color purity whichspaced-apart positioning of the phosphor strips would otherwise haveproduced.

It has also been found that phosphor strips deposited by theaforedescribed process were subject to appreciable variations in densityfrom one phosphor strip to the next or even'from one portion of a singlephosphor strip to another portion of that same strip. By density I meanthe concentration of phosphor particles in a unit volume of exposedphotosensitive gel. Since the intensity of the light which is emittedfrom a beam impinged phosphor region, all other factors being equal,depends upon the number of color centers which is, in turn, a functionof the number of phosphor particles present within this beam impingedregion, the aforementioned variations in density also lead tounpredictable variations in the light emissivities of different portionsof the screen structure, thereby making it Very difficult to achieve asufiiciently high degree of uniformity and reproducibility of colorbalance between the differently colored light emissive phosphor strips.

All of the foregoing remarks apply to the indexing strips as well as tothe colored light emissive phosphor strips. Of course, it will beundersoood that, in the case of the indexing strips, the aforementionedirregularities in strip edges and variations in particle densityafiected their secondary electron emissivity and, consequently, theirutility for the production of uniform indexing indications.

While it has proved perfectly feasible to apply both the phosphor stripsand the indexing strips by exposure from that side of the glasssubstrate which faces the exterior of the tube, there are reasons why itmay be even more advantageous to form this screen structure by exposurefrom the interior of the tube. Chief among these reasons is the factthat exposure from the substrate side which faces the exterior of thetube requires illumination of the indexing material bearing gel throughthe previously deposited aluminum film. A very intense source ofillumination is required to penetrate this aluminum film at all, andthis illumination must be continued for a considerable length of timebefore a layer of gel of suflicient thickness has been exposed andrendered insoluble. If, on the other 4 hand, the several exposures arecarried out entirely from the interior side of the screen structure,then the gel which contains the indexing material will be deposited onthat side of the aluminum film which confronts the source ofillumination so that the light from this source need not penetrate thealuminum film. When one proceeds in thislatter manner, the powerrequirements of the light source and the exposure time are substantiallyreduced and a considerable increase in the efliciency of the entireprocess is realized. On the other hand, if each successive exposure ismade from the interior side of the screen structure then the light fromthe source of illumination must traverse the entire depth of each layerof phosphor and/ or indexing material bearing gel before exposing andrendering insoluble that portion of each of these gel layers which ismost closely adjacent to its supporting material (this being the glass.substrate in the case of the phosphor bearing gel and the aluminum filmin the case of the indexing material bearing gel). It has been foundthat so much light may be lost during traversal of the interveningmaterials that the portions of the gel which are closest to thesupporting material are not exposed suificiently to render themcompletely insoluble. Where that occurs, the washing operation whichfollows each exposurewill remove not only that part of the gel whichwasdeliberately left unexposed but will also dissolve that portion of thegel nearest its substrate which hasbeen, unintentionally underexposedand, with it, the

superposed, sufficiently exposed portions of the gel layers togetherwith the useful materials distributed therein.

.Accordingly, it is a primary object of my invention to provide animproved method of manufacturing screen structures for cathode raytubes;

It is another object of my invention to provide an improved photographicmethod of manufacturing the screen structures of color televisioncathode ray tubes.

It is. still another object of the invention to provide an improvedmethod fo manufacturing cathode ray tube screen structures involving theexposure of selected portions of photosensitive gels in such a manner asto fix particles of different materials in different ones of saidselected portions.

It is a still further object of the invention to provide an improvedphotographic method of manufacturing cathode ray tube screen structureswhereby sharply delineated elements containing particles of certainmaterials with substantially uniform densities are formed.

To achieve the foregoing objects of the invention, as well as otherswhich will appear, there are deposited successive layers ofphotosensitive gel, one for each of the different materials which are tobe formed into screen elements of a desired configuration. However,unlike those of the prior art, these gel layers do not contain thevarious materials at the time of their deposition. Instead, each layerof gel is deposited and portions thereof are selectively exposed whilethis gel still contains no screen forming material. The particularmaterial (phosphor or indexing) whose configuration in the completedscreen structure is determined by the exposure pattern of a given gellayer is deposited on this gel layer only after the same has beenselectively exposed, but before its unexposed portions have been removedby washing. After deposition of this material on a gel layer, theresulting structure is washed and the unexposed gel, together with thematerial deposited thereon, is removed. The material deposited on theexposed gel, on the other hand, will have penetrated the same to someextent and will therefore be trapped inside or will adhere to the outersurface of the gel owing to the tackiness of the latter. In any case,the material deposited on the exposed gel will resist removal by washingand most, if not all of it, will remain in place even after theunexposed gel and the material deposited thereon have been washed away.The same process, involving the successive steps of. depositing gelalone, selectively exposing this gel, depositing screen material thereonand washing off unexposed gel, are carried out in turn for each of thedifierent screen materials which are to be deposited by this photographic process. By proceeding in this manner in accordance with theinvention the edges of the exposed portions of each gel layer are causedto be extremely sharp and well defined. This, I believe, results fromthe absence of particles of screen constituent material from this gellayer during exposure, which would otherwise scatter the lighttraversing the gel layer in undesirable directions.

The density of the screen material which remains in place on the exposedportions of the photosensitive gel after washing is also much moreuniform than in the case where the screen material was distributedthroughout the photosensitive gel for, in my improved method, thisdensity can be controlled by controlling the manner of deposition of thescreen material on the exposed gel layer without concern for variationsin the degree of insolubility of different exposed portions of the gellayer which cause variations in its retentivity for other materialdistributed therein.

Finally, there is now no danger that, if the exposure is made from theinterior surface of the screen structure, the portions of the gel whichare closest to its supporting member will not be properly exposed. Thisis because the gel is substantially translucent and permits light usedfor exposure to penetrate all the way down to the supporting memberwithout undergoing appreciable attenuation.

Details concerning a particular manner of carrying out my improvedmethod of screen manufacturing are presented hereinafter in the courseof the description of the accompanying drawings in which Figure l is anenlarged fragmentary view of a typical cathode ray tube screen for colortelevision reception;

Figure 2 is a simplified, diagrammatic illustration of certain of theequipment used in manufacturing screen structures by photographicmethods; and

Figures 3A to 35. inclusive show an enlarged fragment of the screenstructure illustrated in Figure 2 at various stages of its manufactureby the method which embodies my invention.

The structure of the cathode ray tube screen illustrated in Figure l ofthe drawings, to which more particular reference may now be had, isentirely conventional in all respects, consisting of a glass substratewhich may be either the face plate of the cathode ray tube itself or aseparate glass plate supported within the tube envelope. Upon this glasssubstrate there are disposed a plurality of parallel vertical phosphorstrips, of which those designated 11 are made of a fluorescent materialemissive of red light in response to impingement by the electron beam ofthe cathode ray tube. Those strips designated 12 are made of afluorescent material responsive to electron beam impingement to emitgreen light, while those designated 13 are similarly responsive to emitblue light. As is also conventional, the entire surface area of thesestrips 11, 12 and 13 is covered by a film 14 of a highly reflective,conductive material, such as aluminum, and suficiently thin to bepermeable to the electrons of the cathode ray beam. On the electron beamconfronting side of this aluminum film 14 there are disposed a pluralityof socalled indexing strips 15 which are arranged in a predeterminedgeometrical relationship with respect to the phosphor strips 11, 12 and13 and which are characterized by having a secondary electron emissionratio which differs substantially from that of the aluminum film. Inpractice the indexing strips 15 will frequently be disposed in alignmentwith phosphor strips emissive of light of one particular color, saygreen. There will then be an indexing strip superimposed upon everythird phosphor strip and separated therefrom by the aluminum film 14.However, it will be understood that this particular arrangement ofindexing strips is not essential to my inventive concept, which isconcerned only with the method of forming these indexing strips, as wellas the phosphor strips beneath the aluminum film, and is entirelyindependent of the geometrical configuration thereof. Suitable materialsof which these indexing strips may be made include principally thosehaving high secondary electron emission ratios relative to that of thealuminum film. A variety of materials, such as magnesium oxide, silver,gold, tungsten and various other high atomic Weight materials have thisproperty. It has been explained previously that differences in theintensity of the secondary electron emission current flowing from theseindexing strips and from the bare aluminum film between them, when oneor the other is impinged by the electron beam, are utilized to insurefidelity of color reproduction. It will be understood that, instead ofrelying on differences in secondary electron emissivity between indexingstrips and bare aluminum film, differences in light emissivity betweenthese portions of the screen structure can also be used to produceindexing indications. If this latter form of indexing indications ispreferred then the indexing strips 15 may be made of a phosphor materialrather than of a material having high secondary electron emission ratio.

For the manufacture of such a screen structure as is illustrated inFigure 1 of the drawings, there is required certain precision equipmentwhich is illustrated in simplified form in Figure 2 of the drawings towhich reference may now be had. The apparatus illustrated in Figure 1includes a box-like supporting frame 16 which is preferably of veryrigid construction, as it must support a number of other components inprecise and unvarying alignment relative to each other. At the upper endof this supporting frame 16 there is provided an aperture which isadapted to receive the face plate of a cathode ray tube 18. This faceplate 17 is preferably supported in this aperture by a separate insertframe 16a which is clamped securely around the rim of the face plate ofthe cathode ray tube before the screen forming operations are begun andwhich remains thus mounted on the tube during all of these operations,as hereinafter described. The outer dimensions of this insert frame aresuch that it fits snugly into the aperture in supporting frame 16. Itsfunction is to insure exact repositioning of the tube face with respectto the aperture in, and with respect to other apparatus mounted onsupporting frame 16 after each of the several removals of the bulb fromthis frame which are necessary during screen formation.

If the tolerances required in the manufacture of an insert frame whichfits snugly into the aperture of the supporting frame are deemed toodifiicult to maintain economically then the location of the insert framemay be conveniently determined by means of accurately adjustable stopmembers.

The face plate 17 is placed in this aperture with its exterior surfaceconfronting the interior of the frame 16. While, at this stage of themanufacturing process of the cathode ray tube, the face plate 17 may becompletely severed from the other portions of the cathode ray tube, itis preferred to form this face plate integrally with the flared portion19 which, in the completed tube, connects the neck of the tube to theface plate. In practicing my invention, there is no objection toinserting this face plate into the aperture in supporting frame 16 withits flared portion 19 and its neck 19a attached. This flared portion andthe neck will then extend upwardly above the supporting member 16. Atthe lower end of the supporting frame 16 there is disposed a lightsource 2% which is adapted to illuminate the exterior surface of thescreen structure 17 at the upper end of the supporting member 16.Intermediate the light source 20 and the face plate 17, and as close aspossible to the latter, there is disposed a mask 21 having alternateopaque and translucent portions formed in the same configuration as isdesired for the phosphor and indexing elements of the screen structure.Means are provided,

I point source in every case.

, 7 such as, for example, a micrometer adjustment diagrammaticallyillustrated by crank 22 of Figure 2 for effecting lateral displacementof-this mask relative to the supporting frame 16 and also relative tothe face plate 17 and to light source 20, both of which are stationarywithin this supporting frame.

When it is desired to forma screen structure like that of Figure 1,having phosphor and indexing elements in the form of parallelstrips, thetranslucent portions of the mask 21 will, naturally, also be in the formof parallel strips and the lateral displacement of the mask 21 will becarried out in a direction transverse to the longitudinal dimensions ofthe translucent strips so as to permit illumination, at different times,of difierent laterally disposed strip-like portions of the face plate 17and of any materials deposited thereon. In this connection it is to benoted that the light source for the exposure. technique underconsideration is preferably a However, known point sources provide lightof comparatively low intensity so that their use requires relativelylong periods of exposure. For screen elements having the form of narrowstrip-like portions this exposure period can be shortened by the use ofa more intense line source of light whose long dimension parallels thelong dimension of the translucent portions of mask 21. If, on the otherhand, the phosphor and/ or indexing elements of the screen structure areto take the form of dots whose dimensions measured in all directions aresubstantially the same, then the light source should be as nearly apoint source as possible. I have found in practice that, While a widevariety of suitable light sources are available, good results can beobtained with a high-pressure mercury arc lamp such as, for example,that sold by the General Electric Company under the type number EH6.

The process of forming the individual strip-like elements, using theapparatus of Figure 2, is illustrated for one particular element inFigures 3A through 3E of the drawings to which more particular referencemay now be had. In Figure 3A there is shown a small fragment of the faceplate 17 of Figure 2. Superposed on this face plate is a layer 25 of astock solution of photosensitive gel which may be used equally well forthe deposition of all ofthe different screen constituting materialswhich necessitate photoelectric deposition. Such a stock solution mayconsist, for example, of 25 grams of polyvinyl alcohol in 600 cc. ofdistilled water. Various polyvinyl alcohols of different averageviscosityvalues, and hence of different degrees of polymerization may beused. However I have found that satisfactory results are obtained with apolyvinyl alcohol of medium viscosity such as prepared by Dupont underthe trade name Elvanol 52-22.

The polyvinyl alcohol is added to the distilled water and, withcontinuous stirring at approximately 120'degrees Fahrenheit, iscompletely dissolved in about two to three hours. After filtering thesolution, 200 cc. of ethyl alcohol and 25 cc. of a solution of ammoniumor potassium dichromate containing 22 grams of the salt for each 100 cc.of water are added. The resulting solution is photosensitive and shouldbe kept under subdued light. The application of this photosensitivesolution to the face plate 17 to form the layer 25 thereon may becarried out in any desired manner, as for example, by introducing theliquid into the tube so that it will flow down the wall of the flaredportion 19 of Figure 2 or by spraying it from a nozzle positioned withinthis flared portion 19 near the neck 19a. I have found that a moreuniform layer of this photosensitive material can be produced byspraying and this is how I prefer to apply the material.

After a sufficient thickness of this photosensitive solution, which maybe of the order of .005 to .025 inch, is obtained it is dried thoroughlyin the dark at a relatively cool temperature, i.e. by means of an airblast at a temperature somewhat less than 75 degrees Fahrenheit. Thecoating which is thus formed on the interior surface of the face plate17 is then subjected to illumination from the light source 20 throughthe several translucent portions of the mask 21. The effect which thisillumination has on each illuminated portion of the photosensitive layer25 is illustrated in Figure 33 where the insolubility of the exposedportion is symbolized by the shading of region 26 of the photose nsitivelayer 25. It will be understood that this shading is purely symbolic anddoes not necessarly correspond to any actual change in the lighttransmissive characteristics of the photosensitive layer, which usuallyremains translucent as before. Next, and as illustrated in Figure 3C,there is deposited over both the exposed and unexposed portions of thephotosensitive layer 25 a substantially uniform layer 27 of phosphorparticles of the particular phosphor material which it is desired toform into strips in the locations of the exposed portions 26 of thephotosensitive material. This phosphor layer may be applied by anyconventional technique such as, for example, spraying in a watersuspension, dusting or otherwise. Sufiicient phosphor is preferablydeposited so that the layer 27 contains approximately 0.5 to 6milligrams of phosphor material per square centimeter. As has beenindicated this phosphor forms a layer on or near the surface of thephotosensitive layer and is retained in place by the tacky condition ofthe latter.

Next water is poured into the bulb, agitated and de canted. In thismanner the unexposed portion of the photosensitive layer 27 is dissolvedand removed by decanting, carrying away with it those parts of thephosphor layer 27 which were not deposited on top of an exposed portion26. Neither the amount of water used in this process nor the degree ofagitation thereof are critical. In fact, if it appears by inspectionthat a single washing operation is insufiicient to remove all traces ofthe phosphor particles deposited on unexposed portions of thephotosensitive layer, then this washing action may conveniently berepeated until such complete removal has been obtained. In practice,however, I have found that a single washing operation will usuallysuffice in this process, as distinguished from prior practice where thephosphor was sometimes applied to the glass substrate without theintervening photosensitive layer. The reason for this is that thephosphor particles tend to adhere to the material on which they aredeposited and, if this material happens'to be the glass substrateitself, then they will be difficult to flush away, whereas if, as in thepresent process, the actual supporting medium is the photosensitivelayer, then dissolution of the latter during the washing operation willleave the phosphor particles unsupported and will facilitate theirremoval.

The structure which remains after this washing operation is illustratedin Figure 3D where there is shown the glass substrate 17, the exposedportion 26 of photosensitive material superposed thereon and the portion27a of the phosphor layer 27 which was applied to the exposed portion ofthe photosensitive layer. It is apparent that this washing operation, aswell as other succeeding washing operations, is preferably carried outaway from supporting frame 16. At the end of the washing process,however, the bulb 18 is repositioned in the supporting frame 16preferably in substantially the same position that it occupied duringthe initial exposure through mask 21. While considerable care must beexercised in repositioning this bulb so as to restore it to its'formerposition, it has proven practical, particularly by use of theaforedescribed separate insert frame, to carry out several such removalsand replacements without introducing any appreciable error in bulblocation. Either before or after, but prefgably after the bulb has beenrepositioned in the supporting frame 16, the mask 21 is displaced to anew position such that light emanating from source will be projectedupon portions of the face plate corresponding to the desired locationsof strips of phosphor of a difierent color. The steps illustrated inFigures 3A through 3D are then repeated for this second phosphor andagain, after wash-out and replacement of the bulb and repositioning ofthe mask, for the third phosphor.

Thereafter, the aluminum film 14 of Figure l is applied to thepreviously formed portions of the screen structure in any conventionalmanner, as for example by evaporating a layer of aluminum of suitablethickness onto an organic protective film which has previously beendeposited on the phosphor strips, and also onto the portions of theglass substrate which remain bare between adjacent phosphor strips. Ontop of this aluminum film there is then formed a second organic film inaccordance with the teachings of copending application of Guy F.Barnett, Serial No. 367,181, filed July 10, 1953, and assigned to theassignee of the present invention which deals in detail with thetechnique of applying any particular material over an electron permeablealuminum film. After this second organic film has been applied to thealuminum layer the steps illustrated in Figures 3A through 3D arerepeated once again, using indexing material instead of phosphormaterial. When the foregoing steps have been completed, the tube isbaked until substantially all the organic materials used in the processof screen formation, and which include the remnants of thephotosensitive layers as well as the organic films used in the processof forming the aluminum film, have been substantially completelyvaporized. The remaining portions of the internal tube structure, suchas its electron gun and various internal coatings may then be added.

At the conclusion of the foregoing process a phosphor strip which isformed in the manner illustrated in Figures 3A through 3D has theappearance illustrated in Figure 3E where it is shown to consist simplyof the phosphor material which had been left deposited on the exposedportion of the photosensitive layer after washoif, and which had settledon the glass substrate when the exposed photosensitive material wasvaporized during bake-out.

It will be noted that, in a manufacturing process which uses the rig ofFigure 2, the indexing strips are formed by exposure of photosensitivematerial through the previously formed aluminum film. Since thisaluminum film is substantially less light transmissive than thephotosensitive materials used in the deposition of the phosphor strips,the exposure of the photosensitive material, to which the indexingmaterial is to be applied, must be carried out under much more intensiveillumination and/or for a much greater length of time than the exposureof the photosensitive materials which bear the colored light emissivephosphors. The first alternative increases the complexity of theequipment because provisions must be made for varying the intensity ofillumination produced by the light source 20. The second alternativedelays the completion of the process. While neither of thesecomplications is prohibitive, yet, where speed and efiiciency ofprocessing are of the essence, it may be preferred to use a difierentexposure rig wherein the light source is disposed above the narrow endof the flared tube portion and wherein an appropriately scaled down maskis disposed within this narrow end of the flared portion, between thelight source and the screen. To avoid interference with the illuminationof the screen through the mask it is preferred, in this alternativearrangement, to remove the tube neck before carrying out the variousexposures and to replace it at the end of the process.

The foregoing discussion has been directed to the case where exposure ofthe photosensitive material renders the latter substantially lesssoluble than it was before exposure. In the event that the oppositeeffect should take place and the material be rendered more soluble byexposure then it will be apparent that the method of my invention cancontinue to be practiced provided only that the exposure mask is alignedwith the cathode ray tube face plate during each exposure in such mannerthat those portions which are eventually to be covered with a substanceof the particular kind being deposited are shielded from illumination.

it is apparent that various other alternatives to the method outlined indetail hereinbefore will occur to those skilled in the art withoutdeparting from my inventive concept. Accordingly, I desire the latter tobe limited only by the appended claims.

I claim:

1. The method of forming a cathode ray tube screen structure on a glasssubstrate which is suitable for in corporation in a cathode ray tube asthe screen supporting portion thereof, said method comprising the stepsof: depositing on all areas of said substrate a substantiallytransparent layer of unexposed photosensitive material havingsubstantially different solubility in a predetermined solvent before andafter exposure, exposing throughout the entire depth of said layer thoseportions of said layer deposited on selected areas of said substratethereby to modify the solubility in said solvent of all of thephotosensitive material occupying said last-mentioned selected areas,depositing directly on exposed and unexposed portions of said layersolid particles of a substance which is substantially unafiected bytemperatures at which said photosensitive material vaporizes and whichis responsive to electron beam impingement to emit radiant energy, saidlayer being retentive of said substance at least in its condition oflesser solubility, and subsequently washing the resultant assembly withsaid solvent so as to remove selectively substantially all of saidmaterial constituting those portions of said layer having the greatersolubility and said substance deposited thereon while leaving in placethose portions of said layer having the lesser solubility and saidsubstance deposited on said last-named portions.

2. The method of forming a cathode ray tube screen structure on a glasssubstrate which is suitable for incorporation in a cathode ray tube asthe screen supporting portion thereof, said method comprising the stepsof: depositing on all areas of said substrate a substantiallytransparent layer of unexposed photosensitive material which is solublein a predetermined solvent before ex posure and insoluble in saidsolvent after exposure, exposing throughout the depth of said layerthose portions of said layer deposited on selected areas of saidsubstrate thereby to render insoluble all of the photosensitive materialoccupying said selected areas, depositing directly on exposed andunexposed portions of said layer solid particles of a substance which issubstantially unaifected by temperatures at which said photosensitivematerial vaporizes and which is responsive to electron beam impingementto emit radiant energy, said layer being reteurive of said substancewhen insoluble, and subsequently washing the resultant assembly withsaid solvent so as to remove selectively substantially all of saidmaterial constituting of the soluble portions of said layer and saidsubstance deposited thereon while leaving in place the insolubleportions of said layer and said substance deposited on said last-namedportions.

3. The method of forming a cathode ray tube screen structure on a glasssubstrate which is suitable for incorporation in a cathode ray tube asthe screen supporting portion thereof, said method comprising the stepsof: depositing on all areas of said substrate a first substantiallytransparent layer of unexposed photosensitive material havingsubstantially difierent solubility in a predetermined solvent before andafter exposure, exposing throughout the entire depth of said layer thoseportions of said layer deposited on selected areas of said substratethereby to modify the solubility in said solvent 7 w 11 a r of all ofthe photosensitive material occupying said selectedi'areas, depositingdirectly on exposed and unexposed portions of said layer solid particlesof a first substance which is substantially unatfected by temperaturesat which said photosensitive material vaporizes and which is responsiveto electron beam impingement to emit radiant energy, said layer beingretentive of said substance at least in its conditionof lessersolubility, subsequently washing the resultant assembly with saidsolvent so as to remove selectively substantially all of said materialconstituting those portions of said layer having the greater solubilityand said substance deposited thereon while leaving in place thoseportions of said layer having the lesser solubility and said substancedeposited on said last-named portions, depositing on all areas of thepreviously formed portions of said screen structure a secondsubstantially transparent layer of unexposed photosensitive material,said last-named material having substantially difierent solubility in apredetermined solvent before and after exposure, exposing throughout theentire depth of said second layer those portions of said second layerdeposited on selected areas of said previously formed portions of saidscreen structure thereby to modify the solubility in said solvent of allof the photosensitive material of said second layer occupying saidlast-mentioned'selected areas, depositing directly on exposed andunexposed portions of said second layer solid particles of a secondsubstance which is substantially unafiected by temperatures at whichsaid second photosensitive layer vaporizes and which is responsive toelectron beam impingement to emit radiant energy which is distinctivelydifferent from that of which said first substance is emissive, saidsecond layer being retentive of said second substance at least in itscondition of lesser solubility, and subsequently washing the resultantassembly with said solvent so as to remove selectively substantially allof said material constituting those portions of said second layer havingthe greater solubility and said second substance deposited thereon Whileleaving in place those portions of said layer having the lessersolubility and said second substance deposited on said last-namedportions.

4.-The method of claim 3 further characterized in that all areas of saidpreviously formed portions of said screen structure are coated with alight reflective, electron transmissive metallic layer before depositingsaid second layer of unexposed photosensitive materiah 12 w r 5. Themethod of claim 1 further characterized in that the structure so formedis baked until said photosensitive material is substantially completelyvaporized.

6. 'Ihemethod of claim lturther characterized in that a solvent forjsaidphotosensitive, material is water.

- 7. The method of claim 1 further characterized in that saidphotosensitive material is a water solution of polyvinyl alcohol and adichromate salt.

8. The method of claim- 1 further characterized in that said substrateis of substantially transparent material and in that said exposure iscarried out by illumination through said substrate. 7

' 9. The method of claim 3 further characterized in that said firstandsecond substances are phosphors emissive of light of different colors inresponse to electron impingement.

10. Thern'ethod of claim 9 further characterized in that saidselectively exposed portions of photosensitive material are inthe formof narrow parallel strips.

11. The method of claim 3 further characterized in that said firstsubstance is a phosphor and in that said second substance is a materialhaving a secondary electron emission ratio substantially in excess ofunity.

12. The method of claim 11 further characterized in that said materialof secondary electron ratio in excess of unity is magnesium oxide.

References Cited in the file of this patent UNITED STATES PATENTS ColorTelevision Tubes, Sylvania Technologist, July 1953,

1. THE METHOD OF FORMING A CATHODE RAY TUBE SCREEN STRUCTURE ON A GLASSSUBSTRATE WHICH IS SUITABLE FOR INCORPORATION IN A CATHODE RAY TUBE ASTHE SCREEN SUPPORTING PORTION THEREOF, SAID METHOD COMPRISING THE STEPSOF: DEPOSITING ON ALL AREAS OF SAID SUBSTRATE A SUBSTANTIALLYTRANSPARENT LAYER OF UNEXPOSED PHOTOSENSITIVE MATERIAL HAVINGSUBSTANTIALLY DIFFERENT SOLUBILITY IN A PREDETERMINED SOLVENT BEFORE ANDAFTER EXPOSURE, EXPOSING THROUGHOUT THE ENTIRE DEPTH OF SAID LAYER THOSEPORTIONS OF SAID LAYER DEPOSITED ON SELECTED AREAS OF SAID SUBSTRATETHEREBY TO MODIFY THE SOLUBILITY IN SAID SOLVENT OF ALL OF THEPHOTOSENSITIVE MATERIAL OCCUPYING SAID LAST-MENTIONED SELECTED AREAS,DEPOSITING DIRECTLY ON EXPOSED AND UNEXPOSED PORTIONS OF SAID LAYERSOLID PARTICLES OF A SUBSTANCE WHICH IS SUBSTANTIALLY UNAFFECTED BYTEMPERATURES AT WHICH SAID PHOTOSENSITIVE MATERIAL VAPORIZES AND WHICHIS RESPONSIVE TO ELECTRON BEAM IMPINGEMENT TO EMIT RADIANT ENERGY, SAIDLAYER BEING RETENTIVE OF SAID SUBSTANCE AT LEAST IN ITS CONDITION OFLESSER SOLUBILITY, AND SUBSEQUENTLY WASHING THE RESULTANT ASSEMBLY WITHSAID